Among known techniques for introducing an impurity into a surface layer of a solid sample is a plasma doping method in which an impurity is ionized and introduced into a solid at low energy (refer to Patent document 1, for example). FIG. 11 shows a general configuration of a plasma processing apparatus which is used for a plasma doping method as a conventional impurity introducing method disclosed in the above-mentioned Patent document 1. As shown in FIG. 11, a sample electrode 6 to be mounted with a sample 9 which is a silicon wafer is provided in a vacuum container 1. A gas supply apparatus 2 for supplying a doping material gas including a desired element such as B2H6 to the inside of the vacuum container 1 and a turbomolecular pump 3 for reducing the pressure in the vacuum container 1 are provided, whereby the pressure in the vacuum container 1 can be kept at a prescribed value. Microwaves are radiated from a microwave waveguide 51 into the vacuum container 1 via a quarts plate 52 as a dielectric window. The microwaves interact with a DC magnetic field formed by an electromagnet 53, whereby microwave plasma with a magnetic field (electron cyclotron resonance plasma) 54 is formed in the vacuum container 1. A high-frequency power source 10 is connected to the sample electrode 6 via a capacitor 55 so as to enable control of the potential of the sample electrode 6. A gas that is supplied form the gas supply apparatus 2 is introduced into the vacuum container 1 through a gas inlet 56 and exhausted into the turbomolecular pump 3 through an exhaust hole 11.
In the above-configured plasma processing apparatus, a doping material gas such as B2H6 that is introduced through the gas inlet 56 is converted into plasma 54 by a plasma generating means consisting of the microwave waveguide 51 and the electromagnet 53 and boron ions in the plasma 54 are introduced into a surface layer of a sample 9 by means of the high-frequency power source 10.
A method in which a high-frequency current supplied to a sample electrode is measured has been proposed as a method for controlling a doping amount in a plasma doping method and apparatus. FIG. 12 shows a general configuration of an exemplary apparatus of such a type. As shown in FIG. 12, a sample electrode 6 to be mounted with a sample 9 which is a silicon wafer is provided in a vacuum container 1. A gas supply apparatus 2 for supplying a doping gas including a desired element such as B2H6 to the inside of the vacuum container 1 and a turbomolecular pump 3 for reducing the pressure in the vacuum container 1 are provided, whereby the pressure in the vacuum container 1 can be kept at a prescribed value. High-frequency electric power is supplied to the sample electrode 6 from a power source 10 via a capacitor 55 and a high-frequency current transformer 58, whereby plasma is formed in the vacuum container 1 and boron ions in the plasma are introduced into a surface layer of a sample 9. The doped boron concentration can be controlled by measuring a high-frequency current during a discharge with a current meter 59 via the high-frequency current transformer 58. A counter electrode 57 is opposed to the sample electrode and is grounded (refer to Patent document 2, for example).
MOS transistors, for example, are produced by forming a metal wiring layer on the sample 9 into which the impurity ions have been introduced in the above-describe manner, forming a thin oxide film on the metal wiring layer in a prescribed oxidizing atmosphere, and then forming gate electrodes on the sample 9 with a CVD apparatus or the like. However, in forming transistors, activation processing needs to be performed after the introduction of impurity ions by the plasma doping. The activation processing is processing of re-crystallizing an impurity-introduced layer by heating it by RTA (rapid thermal annealing), spike RTA, laser annealing, flash lamp annealing, or the like. A shallow activation layer can be obtained by heating a very thin impurity-ion-introduced layer effectively. To heat a very thin impurity-ion-introduced layer effectively, processing for increasing, before introduction of impurity ions, the absorbance of light emitted from a light source such as a laser or a lamp of a very thin layer into which to introduce impurity ions is performed. This processing, which is called “pre-amorphization,” is as follows. In a plasma processing apparatus which is similar in configuration to the above-described ones, plasma of a He gas, for example, is generated and generated He ions, for example, are caused to be accelerated toward and collide with a substrate by a bias voltage, whereby the crystal structure of a substrate surface layer is destroyed to attain amorphization. This technique has already been proposed by the inventors of this application (refer to Patent document 1, for example).
Patent document 1: U.S. Pat. No. 4,912,065
Patent document 2: Japanese Patent No. 2,718,926
Non-patent document 1: Y. Sasaki et al., “B2H6 Plasma Doping with In-situ He Pre-amorphization,” 2004 Symposia on VLSI Technology and Circuits.